The present invention relates generally to image processing and more specifically to a geometric deformation correction method and system for dot pattern images.
Bar-codes are information carrying graphical patterns designed for easy and reliable automatic retrieval. The most common bar-codes are known as one-dimensional bar-codes. These graphical patterns vary in a single dimension (e.g. the horizontal dimension), and are constant in the other dimension (e.g., the vertical dimension). One-dimensional bar-codes are employed in low information content applications like product index registry (e.g. automatic price tagging and inventory management), or serial number registry (e.g. test-tube tagging in automated medical tests). Common examples of one-dimensional bar-codes are those bar-codes that are affixed or printed on the packages of items purchased at a supermarket or other store. These bar-codes typically can only encode limited information, such as the price of the item and the manufacturer. The items having the bar-codes are scanned at a checkout counter to facilitate the tallying up of a total receipt.
In order to convey more information on the same surface area, two-dimensional bar-codes were developed. Two-dimensional bar-codes involve intricate patterns that vary in both the horizontal and the vertical dimensions. Two-dimensional bar-codes are used in applications that require more information content. For example, two-dimensional bar-codes can be used to encode mail addresses for automated mail reading and distribution systems. Mail carrier companies can use the two-dimensional bar code on shipping packages to encode shipper information, recipient information, tracking information, etc. In another example, two-dimensional bar-codes can be used to encode the compressed content of a printed page to avoid the need for optical character recognition at the receiving end.
Two-dimensional bar-codes are typically graphical patterns composed of dots that are rendered by using two-toned dots (e.g. black dots on a white background). These dots usually occupy a rectangular area. Most current systems use a bar-code printer to print an original bar-code, and the bar-code readers detect that original bar-code. However, it is desirable in many office applications to have a bar-code system that can scan and reliably recover information from copies of the original bar-code. For example, if the original bar-code is embedded in an office document and is given to a first worker, and the first worker desires to share the document with a co-worker, it would be desirable for the first worker to copy the document and provide the same to the co-worker having confidence that the information embedded in a bar-code in the document could be recovered by the co-worker if needed.
Unfortunately, the prior art bar-code and bar-code reading systems cannot reliably recover information encoded in the bar-code except from an original bar-code that is newly printed by a bar-code printer. For example, most systems have difficulty in reliably reading and recovering information from a bar-code that is a photocopy of the original. Moreover, prior art systems have an even greater difficulty in accurately reading and recovering information from a bar-code that is a photocopy of another photocopy of the bar-code (e.g., a bar-code that has been photocopied two or more times).
Accordingly, a challenge in the design of 2D bar-codes and systems to read such bar-codes is to develop a scheme that can produce bar-codes and reliably recover information from bar-codes, even after successive copies of the original, using office equipment. In other words, the system needs to be designed in such a way as to compensate for degradation of the bar-code, thereby making such a system robust. In summary, it is desirable that a bar-code design and bar-code system be designed in such a way as to ensure that the bar-codes can be recognized and the encoded information recovered even after successive copying and handling in a paper path.
The bar-code pattern is often degraded between the time of creation and its use. These degradations can include contrast reduction, stains, marks, and deformations. Many degradations can be corrected by utilizing one or more traditional methods, such as contrast enhancement, adaptive thresholding, and error-correction coding. However, geometric pattern deformation remains a challenge and does not lend itself to resolution by prior art methods. Geometric pattern deformation can occur, for example, when a pattern is photocopied.
The photocopying process can inject the following types of geometric deformations to the dots in a bar-code pattern. The first type of geometric deformations is shape deformations. Shape deformations cause the dots to change their size either shrinking or expanding the dots. Shape deformations typically depend on the brightness setting of the copier. For example, when the brightness setting is set to a darker setting, the dots tend to expand. When the brightness setting is set to a lighter setting, the dots tend to shrink.
The second type of geometric deformations is space deformations. Space deformations cause the dots corresponding to certain coordinates in the original image to be located at different coordinates in the copy. There are two types of space deformations: global deformations and local deformations. Global shape deformations, such as translation, rotation or affine, are those that change the coordinates of the dots in a way that is consistent with an equation that describes the deformations for the entire image. There are also local space deformations that are deformations that cannot be modeled as a global space deformation. These local space deformations are especially difficult to characterize and correct.
Accordingly, there remains a need for a method for correcting geometric deformations in bar-code patterns that overcomes the disadvantages set forth previously.
It is an object of the present invention to provide a method for correcting geometric deformations in a bar-code pattern.
It is another object of the present invention to provide a method for correcting shape deformations in a bar-code pattern.
It is a further object of the present invention to provide a method for correcting space deformations in a bar-code pattern.
A method and system for correcting geometric deformations in an aligned image. A shape deformation correction unit is provided for receiving the aligned image and based thereon for generating a shape-corrected image. A space deformation correction unit is coupled to the shape deformation correction unit and receives the shape-corrected image. The space deformation correction unit uses the shape-corrected image to generate edges and interfaces, and further generates a corrected image based on the interfaces and the shape-corrected image.